The invention relates to a machine for processing flat articles, and in particular postal items, the machine comprising a conveyor path extending from one of its ends in a substantially horizontal direction to bring a stack of articles standing edge-on towards an unstacking head, an unstacking head close to said end and extending in a substantially vertical direction to unstack a first article from the stack which presents with its free face parallel to the unstacking head, and a mechanical jogging device for jogging at least the first article of the stack prior to unstacking thereof against a jogging margin that extends in a direction substantially perpendicular to the conveyor path and to the unstacking head.
Such a machine is commonly used for sorting a large quantity of postal items. In this type of machine, a jogging device is used since the postal items are not all of the same dimensions and each item to be unstacked must be positioned (with reference to a jogging margin) relative to the unstacking head prior to being unstacked. If such an operation is not performed, two successive postal items may be unstacked simultaneously (double-pickoff phenomenon). To prevent such double-picking-off, the jogging device pushes each item to be unstacked against a reference plane which extends generally transversely to the item that is to be unstacked and which is called the jogging margin.
In a known postal sorting machine, the mechanical jogging device includes a screw having a pitch greater than unity that co-operates with interposed fingers. The screw is installed in line with the conveyor path up to the unstacking head. The items in the stack are pre-separated by the interposed fingers as they travel between the rotating screw threads. The interposed fingers act to form bundles of mail of greater or lesser size along the screw up to the vicinity of the unstacking head. The mail items in the smaller bundles splay out between the interposed fingers and are jogged against the jogging margin by the friction effect where they rub against the outside surface of the screw.
It is necessary to pre-separate the items in the stack prior to jogging in order to ensure that all of the items in the stack are jogged prior to being unstacked by the unstacking head. This function of pre-separating the items in the stack prior to jogging requires the screw to be of substantial length, thus leading to the jogging device being of considerable length. Such a jogging device is also complex. Furthermore, the leading articles in the stack, which articles have been jogged, have the following articles in the stack pressed against them under drive from the screw. This can result in double-pickoff effects when unstacking occurs.